There are many industrial environments where explosive atmospheres are present due to the nature of the products produced or processed. Facilities such as oil refineries, gas processing plants, mines, grain elevators, etc. are some examples of such environments where electrical discharges must be tightly controlled in order to prevent explosions.
Over the years standards have been developed to insure electrical products which minimize the potential for electrical discharges such as sparks or arcs. Through a design process of careful component selection, proper pc board trace spacing, appropriate dielectric insulation, etc. products can be produced which can be safely used in these hazardous environments.
In order to develop safety requirements for these various hazardous environments a series of classifications have been developed to categorize them. For example Class 1 hazardous environments include those containing flammable gases, vapors or liquids; Class 2 includes combustible dusts; Class 3 includes ignitable fibers. Environments where those explosive atmospheres are abnormally present are further classified as Division 2 environments, whereas those explosive atmospheres are normally present are classified as Division 1 environments. Therefore, an environment which consisted of flammable gases which were sometimes present would be considered a Class 1 Division 2 area.
As with any type of environment, lighting is an important element. Lighting serves multiple purposes with two applications in particular of interest in this application: signaling and general illumination. Signaling is the use of lighting to indicate some state or presence. Obstruction lighting used to indicate the presence of towers and buildings to aircraft is one example (e.g. beacons used on the tops of radio transmission towers). General illumination lighting is that lighting used to make objects and spaces visible in dark environments (e.g. walkway lights used to illuminate gantries and ladders in refineries). And for those locations where explosive atmospheres could be present, a lighting fixture which is resistant to exposing electrical discharges would be advantageous. Present designs for these devices typically use traditional light sources such as incandescent, fluorescent, or gas discharge lamps. Such sources while providing good photometric properties have a major disadvantage of limited lifetime. The average lifetimes typically range from 1 k to 20 k hours for traditional light sources. Furthermore, such sources are often quite expensive when they are manufactured to meet safety requirements for various hazardous environments.
Therefore, there is a need for a light source that is capable of providing a longer lifetime while operable in a hazardous location.